The steady-state thermal and air-flow resistance performances of horizontally-based pin-fin assemblies have been investigated experimentally. The effects of varying the geometrical configurations of the pin-fins and the air-flow rates have been studied The optimal pin-fin separation S(x)opt in the span-wise direction, to achieve a maximum rate of heat transfer from the assembly, is 1.0 +/- 0.2 mm less-than-or-equal-to S(x) less-than-or-equal-to 3.0 +/- 0.2 mm for the pin-fins arranged either in the in-line or the staggered array. The optimal pin-fin separations in the stream-wise direction for these two arrays are 7.6 +/- 0.2 mm and 7.8 +/- 0.2 mm respectively. The general correlation of the data is : Nu = 0.355 (S(x)/X)0.0446 (S(y)/L)0.048 Re0.585.